Role of arachidonic acid metabolism in transcriptional induction of tumor necrosis factor gene expression by phorbol ester.

The treatment of human HL-60 promyelocytic leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with induction of tumor necrosis factor (TNF) transcript. The study reported here has examined TPA-induced signaling mechanisms responsible for the regulation of TNF gene expression in these cells. Run-on assays demonstrated that TPA increases TNF mRNA levels by transcriptional activation of this gene. The induction of TNF transcripts by TPA was inhibited by the isoquinolinesulfonamide derivative H7 but not by HA1004, suggesting that this effect of TPA is mediated by activation of protein kinase C. TPA treatment also resulted in increased arachidonic acid release. Moreover, inhibitors of phospholipase A2 blocked both the increase in arachidonic acid release and the induction of TNF transcripts. These findings suggest that TPA induces TNF gene expression through the formation of arachidonic acid metabolites. Although indomethacin had no detectable effect on this induction of TNF transcripts, ketoconazole, an inhibitor of 5-lipoxygenase, blocked TPA-induced increases in TNF mRNA levels. Moreover, TNF mRNA levels were increased by the 5-lipoxygenase metabolite leukotriene B4. In contrast, the cyclooxygenase metabolite prostaglandin E2 inhibited the induction of TNF transcripts by TPA. Taken together, these results suggest that TPA induces TNF gene expression through the arachidonic acid cascade and that the level of TNF transcripts is regulated by metabolites of the pathway, leukotriene B4 and prostaglandin E2.